Multimodulation transmitter

ABSTRACT

The present invention discloses a double TRU (Transceiver Unit) ( 45 ). The output signals from the power amplifiers ( 64, 84 ) are combined to one common output signal provided to an antenna arrangement ( 91 ). A DSP (Digital Signal Processor) ( 52, 72 ) of each TRU ( 50, 70 ) comprises means for a constant-envelope modulation scheme ( 54, 74 ) and a non-constant envelope scheme ( 53, 73 ). The DSP:s ( 52, 72 ) select the modulation scheme according to modulation information ( 49, 69 ). In such a way, a switching between different modulation schemes can be performed even on a time-slot basis. For non-constant-envelope modulation, the modulated signal is separated into two component signals. Each TRU ( 50, 70 ) takes care of the amplification of one component. A phase compensation of at least one of the TRU:s ( 50, 70 ) is performed in order to correct for different paths of phases of the power amplifiers ( 64, 84 ). The non-constant envelope modulated signal can also be a multi-carrier signal, e.g. of two or more constant-envelope signals. Also a TCC (Transmitter Coherent Combining) operation is achievable.

TECHNICAL FIELD

The present invention relates in general to wireless communication andin particular to wireless communication transmitter systems.

BACKGROUND

In conventional GSM (Global System for Mobile Communication), amodulation scheme according to GMSK (Gaussian Minimum-Shift Keying) isimplemented. GMSK is a constant envelope modulation scheme, where aphase shift is differentially dependent on the bit sequence. The GMSKmodulation has been chosen as a compromise between fairly high spectrumefficiency and reasonable demodulation complexity.

EDGE (Enhanced Data for Global Evolution) is a high-speed mobile datastandard, intended to enable second-generation GSM and TDMA (TimeDivision Multiple Access) networks to transmit data up to 384 kbps. EDGEprovides the speed enhancement by changing the type of modulation usedand making better use of the carrier currently used. It enables agreater data transmission speed to be achieved in good conditions, inparticular near the base stations by implementing 8PSK(Eight-Phase-Shift Keying) modulation. The 8PSK modulation scheme is ahigh transmission modulation based on phase shift coding. The modulationis of a non-constant envelope type. EDGE can co-exist with the existingGSM traffic, switching to EDGE mode when appropriate.

When upgrading a base station to handle EDGE, the transmitter system hasto be modified. A transmitter used for standard GSM purposes is designedfor supporting GMSK, which means that the power amplifier that are usedtypically are more or less non-linear. When implementing 8PSK, theenvelope may vary in a pre-defined way over time, and non-linearamplification can not be accepted. Thus, in a general case, a newparallel transmitter arrangement has to be provided. Since thetransmitter devices are costly, parallel transmitter arrangements, whichare only used one at a time, means a poor utilization of installedequipment. Furthermore, highly linear power amplifier elements orarrangements are very expensive and there is a request to avoidsolutions using such elements.

In “Increasing the talk-time of mobile radios with efficient lineartransmitter architectures” by S. Mann, M. Beach, P. Warr and J.McGeehan, Electronics & Communication Engineering Journal, April 2001,Vol. 13, No. 2, pp. 65-76, the relationship between linearizing methodsfor power amplification in radio transmitters and efficiency isdiscussed. LINC (LInear Nonlinear Component), known in prior art e.g. byU.S. Pat. No. 5,990,734, is one of the investigated schemes, where onenon-constant envelope signal is divided into two constant envelopesignals, which subsequently can be amplified by non-linear amplifiers.However, since such a method requires two non-linear amplifiers, this isnot a particularly efficient approach for systems also handling constantenvelope signals.

SUMMARY

An object of the present invention is to provide for using one and thesame transmitter system for constant-envelope as well as non-constantenvelope modulation schemes. Another object is to provide a transmittersystem for non-constant envelope modulation schemes based on non-linearpower amplifier elements. A further object of the present invention isto provide the possibility for fast switching between differentmodulation schemes.

The above objects are achieved by methods and devices according to theenclosed claims. In general words, a double TRU (Transceiver Unit) isused. The output signals from the power amplifiers are combined to onecommon output signal provided to an antenna arrangement. A DSP (DigitalSignal Processor) of each TRU comprises means for a constant-envelopemodulation scheme and a non-constant envelope scheme. The DSP:s selectthe modulation scheme according to modulation information providedtogether with the input digital signal. In such a way, a switchingbetween different modulation schemes can be performed even on atime-slot basis.

In case of a non-constant-envelope modulation, the DSP divides themodulated signal into two component signals. Each TRU takes care of theamplification of one component, and the components are eventuallycombined before provided to the antenna arrangement. A phase LOcompensation of at least one of the TRU:s is performed in order tocorrect for different paths or phase positions of the power amplifiers.The non-constant envelope modulated signal can also be a multi-carriersignal, e.g. of two or more constant-envelope signals.

For normal constant-envelope modulation, the two TRU:s are operatingindependently of each other, and the two output signals are combined toa double-carrier signal.

The arrangement can also be operated according to TCC (TransmitterCoherent Combining) of constant-envelope modulated signals, where bothTRU:s are provided with the same digital signal. The two amplifiedoutput signals are combined to create an output signal of double theamplitude. Also here, phase compensation is necessary.

The phase compensation is preferably determined by monitoring the outputpower or monitoring the power in the load of the hybrid and comparingwith expected output power. In one embodiment, a calibration of thephase compensation is performed during TCC bursts, and utilized duringnon-constant envelope modulation. Other embodiments utilize constantamplitude portions of non-constant envelope time slots for performingphase compensation calibration. One may then make use also of powermeasurements of the output signals from each power amplifier. The phasecompensation calibration can also be performed during well-characterizedtraining sequences within the time slots.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a vector diagram illustrating a constant envelope signal;

FIG. 2 is a vector diagram illustrating a non-constant envelope signal;

FIG. 3 is a vector diagram illustrating principles of separating anarbitrary signal into two constant envelope signals;

FIG. 4 is a vector diagram illustrating the principles of transmittercoherent combining;

FIG. 5 is a vector diagram illustrating the effect of phase errors intransmitter coherent combining;

FIG. 6 is a block diagram illustrating an embodiment of a doubletransmitter unit according to the present invention;

FIG. 7 is a flow diagram illustrating an embodiment of a method forproviding two constant envelope modulated signals according to thepresent invention;

FIG. 8 is a flow diagram illustrating an embodiment of a method forproviding a non-constant envelope modulated signal according to thepresent invention;

FIG. 9 is a flow diagram illustrating an embodiment of a methodproviding transmitter coherent combining according to the presentinvention;

FIG. 10 is block diagram illustrating another embodiment of a doubletransmitter unit according to the present invention;

FIG. 11 is a flow diagram illustrating another embodiment of a methodfor providing a non-constant envelope modulated signal according to thepresent invention;

FIG. 12 is a flow diagram illustrating another embodiment of a methodproviding transmitter coherent combining according to the presentinvention;

FIG. 13 is a diagram illustrating a power versus time mask for an 8PSKmodulated normal burst;

FIG. 14 is a block diagram of a part of yet another embodiment of adouble transmitter unit according to the present invention;

FIG. 15 illustrates a time slot used in GMSK or 8PSK modulation;

FIG. 16 is a block diagram illustrating an alternative phase shiftersolution applicable to the present invention;

FIG. 17 is a diagram illustrating the principles of the phase shifter ofFIG. 16;

FIG. 18 is a block diagram illustrating a part supporting frequencyhopping of an embodiment of the present invention;

FIG. 19 is an illustration of a storage of phase shifts usable togetherwith the present invention; and

FIG. 20 is a block diagram of one transmitter unit supporting doublecarrier signals of an embodiment of a double transmitter unit accordingto the present invention.

DETAILED DESCRIPTION

A signal modulated according to the GMSK modulation scheme can bevisualized in the complex signal plane as illustrated in FIG. 1. Thecoordinate system is here supposed to rotate synchronously with the basefrequency of the carrier, and only the phase differences will thereforeappear in the diagram. A modulated signal is thereby represented by avector 10. In GMSK, the phase shift is adjusted according to threesuccessive bits in the digital input signal. Generally speaking, thephase is smoothly shifted π/2 if the three successive digits are thesame. This means that the vector 10 shifts counterclockwise according toarrow 11 if the successive digits are the same and clockwise accordingto arrow 12 if they are different. All the time, the so vector 10maintain its magnitude, i.e. the end of the vector 10 always travels ona circle 13 in the I-Q-space. The modulation scheme is therefore said tobe a constant-envelope scheme. It is relatively easy to amplify aconstant-envelope signal, since also non-linear power amplifiers may beused. Since the signal always has one and the same envelope, the gain isalways the same, regardless of the linearity of the amplifier. Simplerpower amplifier solutions can thereby be used.

A signal modulated according to the 8PSK modulation scheme can be alsobe visualized in the complex signal plane as illustrated in FIG. 2. Thecoordinate system is also here supposed to rotate synchronously with thebase frequency of the carrier, and only the phase differences willtherefore appear in the diagram. A modulated signal is therebyrepresented by a vector 20. In 8PSK, the phase shift is a coding of atriplet of binary digits. A certain phase shift corresponding to aspecific set of digits, as indicated by points 21 in the figure.Depending on the scheme, the assignment may vary, and there might alsobe an offset phase shift present, which removes the points from theaxes. However, the example in FIG. 2 illustrates well the principle.When changing from one triplet to the next, the vector moves from onepoint 21 to another and passes thereby through the interior of thecircle 13. The modulation scheme is therefore said to be anon-constant-envelope scheme. When amplifying an 8PSK signal, theamplifier arrangement has to have relatively linear characteristics,since the signal will change its magnitude. Highly linear amplifiers areexpensive and simpler solutions are desired.

One possible approach to provide a linear amplification is to decomposeor separate the signal into two component signals, amplify thesecomponent signals and combine the amplified component signals again. Ifone keeps the component magnitudes constant, even non-linear amplifierscan be used. This principle, LINC (LInear Nonlinear Component)amplifier, is known in prior art, e.g. by U.S. Pat. No. 5,990,734. Onethereby trades one linear amplifier for two non-linear ones, plus aseparator and combiner. FIG. 3 illustrates the principles. A signal tobe amplified is represented by a vector 30. The vector 30 has a varyingsize S and phase shift φ. The vector 30 is separated into two componentvectors 31, 32. In a first embodiment, the amplitude A of the componentsis the same and follows the circle 13. This amplitude has to be at leasthalf of the maximum amplitude of the vector 30. Also the phasedifference a to the vector 30 is the same, however, directed in oppositedirections. According to basic geometrical considerations, the componentphase shifts θ₁ and θ₂ are specified by:θ₁ =φ−arccos(S/2A)θ₂ =φ+arccos(S/2A)

As anyone skilled in the art understand, it is by this possible toexpress any arbitrary vector of length ≦2A by two component vectors oflength A. The component signals can then be amplified according toprinciples of amplifying constant-envelope signals.

In a more general case, the amplitudes of the components may bedifferent and may also vary depending on the size and phase of thevector 30. Such applications will be discussed more in detail below.

A special case of combining two component signals into one final outputsignal is in case two component signals always with the same phase arecombined. This can be used in cases where a high amplification isdesired, and where it is difficult to achieve by only one amplifier. Asshown in FIG. 4, two components 41, 42 (seen as one vector in thefigure) of the same phase can then be amplified separately and combinedinto an output signal 43. This is the basic idea of TCC (TransmitterCoherent Combining).

A practical problem in combining two separate signals into one outputsignal is that the paths through the amplifiers typically involves somepath difference or that the devices are locked in different phasepositions, which will be noticed as a small phase shift between the twocomponent signals. Such a situation is illustrated in FIG. 5. A signal30 is separated into two components 31, 32. During amplification, thefirst one of the components is shifted AO compared to the second one.This phase shifted components is illustrated by a broken arrow 34. Theactual composed output signal 33 will then be changed both in phase andamplitude. One solution is to measure the phase shift differencecarefully and compensate for it by introducing phase altering means inone of the paths. However, such a phase shift may also be slowly varyingwith time, and in such cases, an adaptive phase compensating arrangementhas to be introduced. A preferred embodiment of such an arrangement willbe described farther below.

An embodiment of a double transmitter unit arrangement 45 according tothe present invention is illustrated in FIG. 6. A first modulation unit50 has an input 51 for receiving a digital signal to be transmitted. Theinput 51 is connected to a DSP (digital signal processor) 52. The DSP 52comprises modulation means; a 8PSK modulator 53 and a GMSK modulator 54.The DSP 52 also comprises a control input 49 for receiving modulationinformation, and a selector 55. The selector 55 selects one of themodulators 53, 54 according to the modulation information received bythe control input 49. The digital signal received by the input 51 isthereby provided to one of the modulators 53, 54. The different means inthe DSP 52 are implemented as software.

The GMSK modulator 54 modulates the input digital signal according tothe GMSK scheme. The modulated signal is in this embodiment provided ina real I and an imaginary part Q at two outputs, connected to ananalogue signal generator 56. In this embodiment, the analogue signalgenerator 56 comprises essentially a quadrature modulator 57. Theanalogue signal generator 56 comprises in turn two DAC's(Digital-to-Analogue Converters) 58, 59 converting the I and Q signals,respectively, into analogue voltages. The analogue voltages aremodulated in a mixer 60 with the carrier frequency, provided by afrequency generator 61, and combined. A phase shifter 62 shifts thefrequency signal to the Q component by 90 degrees. The output from theanalogue signal generator 56 is thus an analogue voltage signal beingmodulated, in this case according to the GMSK scheme.

A phase shifter 63 is in this embodiment connected between themodulators 53, 54 and the quadrature modulator 57. The function of thisunit will be described more in detail further below. The analogue signalfrom the analogue signal generator 56 is provided to a power amplifier64 for amplification. In the present embodiment, the power amplifier 64is a non-linear amplifier. The amplified signal from the output of thepower amplifier 64 is provided to an input of a hybrid combiner device90.

The output of the 8PSK modulator 53 is provided to a separator 65. Theseparator separates the signal provided from the 8PSK modulator into twocomponents, whereby the input signal is the vector sum of the twocomponents. A first one of the components is provided to the input ofthe analogue signal generator 56, in the form of an I and a Q signal. Inthe present embodiment, the second component is terminated. The firstcomponent is processed in the analogue signal generator 56 in the samemanner as described above.

A second modulator unit 70 is very similar to the first modulation unit50. It has an input 71 for a digital signal and a control input 69. ADSP 72 comprises analogously a 8PSK modulator 73 and a GMSK modulator74, and a selector 75 selecting which of the modulator that is going tobe used.

The GMSK modulator 74 is similarly connected to an analogue signalgenerator 76, having a quadrature modulator 77. However, no phaseshifter is present. The quadrature modulator 77 is of the same structureas the one in the first modulation unit 50.

The analogue signal from the analogue signal generator 76 is provided toa power amplifier 84 for amplification. In the present embodiment, thepower amplifier 84 is a non-linear amplifier of the same type as thepower amplifier 64. The amplified signal from the output of the poweramplifier 84 is provided to a second input of the hybrid combiner device90.

The output of the 8PSK modulator 73 is provided to a separator 85,having the same function as the separator 65. The separator 85 separatesthe signal provided from the 8PSK modulator into two components, wherebythe input signal is the vector sum of the two components. In the presentembodiment, the first component is terminated. The second component isinstead provided to the input of the analogue signal generator 76, inthe form of an I and a Q signal. The second component is processed inthe analogue signal generator 76 in the same manner as described above.

The hybrid combiner device 90 combines the two signals provided by theoutputs of the two power amplifiers 64, 84 into a transmitter signal,that is provided to a transmitted device 91. The input power supplied bythe power amplifiers 64, 84 is at least to a part provided as atransmitter signal power. However, any remaining power will bedissipated by a hybrid load 92.

In the present embodiment, the power dissipated over the hybrid load 92is is measured by a power meter 93. The output of the power meter 93 isconnected to the phase shifter 63 via an ADC (Analogue-to-DigitalConverter). The value of the hybrid load power is provided to a phasecontroller 94, which calculates any phase shift between the amplifiedsignals provided to the hybrid. The phase shifter 63 further comprises acomplex multiplier 95, providing a digital phase shift angle e^(iΔθ) tothe I and Q signals respectively. This phase shift is thus in a complexmanner incorporated in the I and Q signals that are entering into theanalogue signal generator 56.

By this double transmitter unit arrangement 45, a number of differentmodulation techniques can be employed. By accompanying the digitalsignals with associated modulation information, the switching betweendifferent modulation schemes can be performed very swiftly, even on atime slot basis. Such an arrangement thus allows the transmitterarrangement 45 to allow for mixing e.g. GMSK bursts with 8PSK traffic ona time slot basis.

Some examples of different operation modes of the double transmitterunit 45 are given here below. Assume normal GMSK traffic. The doubletransmitter unit 45 then operates as two independent transmitter paths,having one carrier each. A digital signal of a first carrier is providedto the first modulation unit 50, while a digital signal of a secondcarrier is provided to the second modulation unit 70. The modulationinformation instructs both DSP's 52, 72 to select a GMSK modulation. Thetwo carrier signals are combined in the hybrid combiner 90 into a commonsignal, provided to the transmitter. The phase shifter arrangement is inthis case not used.

In case a GMSK signal with a high output power is desired, a TCCarrangement can be achieved. In such a case, the same digital signal isprovided to both modulation units 50, 70 together with a request forGMSK modulation. Both transmitter units are processing the same signaland the combined signal at the hybrid combiner 90 output is ideally ofdouble the output power. In comparison with combining two differentcarriers, the TCC carrier is provided with a power four times higher.This is due to the fact that half the power dissipates in the load whencombining two different carriers, while coherent combining removes allpower from the load. However, as discussed above, any phase shiftscaused by path differences in the two branches may deteriorate the totalsignal. In this TCC arrangement, the phase shifter 63 comes into use. Inthis embodiment, the power over the hybrid load 92 is measured. If theamplifier branches are perfectly aligned in phase, all power will bedistributed to the transmitter device 91, which means that no power willbe dissipated through the hybrid load. By adjusting the phase of thesignal in one of the paths, the hybrid load power can be minimized,which indicates an alignment in phase of the two components.

A third operational mode is when a 8PSK signal is to be transmitted.Also in this case, both inputs 51, 71 are provided with the same digitalsignal. This signal will be modulated according to the 8PSK scheme sincethe selectors 55, 75 selects the 8PSK modulator 53, 73. The separator 65in the DSP 52 of the first modulation unit 50 provides a first componentsignal to the analogue signal generator 56. The separator 85 in the DSP72 of the second modulation unit 70 provides instead a second componentsignal to the analogue signal generator 76. The vector sum of these twocomponents equals the original 8PSK-modulated signal. Each of thecomponents are amplified in a separate power amplifier 64, 84, andcombined in the hybrid combined device 90 to form an amplified versionof the original signal. The double transmitter unit arrangement 45 thushere operates at least partly in accordance with the LINC concept,providing one 8PSK carrier signal. Also here, phase shifts between thepaths may appear. Different approaches for solving this problems arediscussed further below.

In FIG. 7-9, the above operations are illustrated as flow dialects.First, in FIG. 7, an embodiment of a method of providing two GMSKsignals on one carrier each according to the present invention isillustrated. The procedure starts in step 100. In step 101, a firstdigital signal is provided to a first transmitter unit. This firstdigital signal is intended to be transmitted on a first carrier. In step102, a second digital signal is provided to a second transmitter unit.This second digital signal is intended to be transmitted on a secondcarrier. In step 103, constant-envelope modulation information isprovided to the first transmitter unit. In step 104, constant-envelopemodulation information is provided to the second transmitter unit. Aconstant-envelope modulation scheme is selected and applied in the firsttransmitter unit according to the modulation information in step 105,and a constant-envelope modulation scheme is selected and applied in thesecond transmitter unit according to the modulation information in step106. A first analogue signal corresponding to the first digital signalmodulated according to the information is generated in step 110. Asecond analogue signal corresponding to the second digital signalmodulated according to the information is generated in step 111. In step112, the first analogue signal is amplified and in step 113, the secondanalogue signal is amplified. In step 114, the two amplified signals arecombined to a two-carrier output signal to be transmitted. The procedureis ended in step 115.

FIG. 8 illustrates an embodiment of a method of providing a signalmodulated according to a 8PSK modulation according to the presentinvention is illustrated. The procedure starts in step 120. In step 121,a digital signal is provided to a first transmitter unit and the samedigital signal is also provided to a second transmitter unit. In step123, non-constant-envelope modulation information is provided to thefirst transmitter unit and to the second transmitter unit. Anon-constant-envelope modulation scheme is selected and applied in thefirst transmitter unit according to the modulation information in step125, and a non-constant-envelope modulation scheme is selected andapplied in the second transmitter unit according to the modulationinformation in step 126. In step 127, the modulated signal in the firsttransmitter is separated into a first and a second component. In step128 the modulated signal in the second transmitter is separated into thesame first and second components. The first component is phase shiftedin step 129 to compensate for differences in phase characteristicsbetween the paths through amplifier stages of the first and secondtransmitter unit, respectively. A first analogue signal corresponding tothe first phase-shifted component is generated in step 130. A secondanalogue signal corresponding to the second component is generated instep 131. In step 132, the first analogue signal is amplified and instep 133, the second analogue signal is amplified. In step 134, the twoamplified signals are combined to a single-carrier output signal to betransmitted. The procedure is ended in step 135.

FIG. 9 illustrates the case of a TCC operation. The procedure starts instep 140. In step 141, a digital signal is provided to a firsttransmitter unit and the same digital signal is provided also to asecond transmitter unit. This digital signal is intended to betransmitted with a double intensity. In step 143, constant-envelopemodulation information is provided to the first transmitter unit and tothe second transmitter unit. A constant-envelope modulation scheme isselected and applied in the first transmitter unit according to themodulation information in step 145, and a constant-envelope modulationscheme is selected and applied in the second transmitter unit accordingto the modulation information in step 146. The first modulated signal isphase shifted in step 149 to compensate for differences in phasecharacteristics between the paths through amplifier stages of the firstand second transmitter unit, respectively. A first analogue signalcorresponding to the first digital signal modulated according to theinformation and phase-shifted is generated in step 150. A secondanalogue signal corresponding to the second digital signal modulatedaccording to the information is generated in step 151. In step 152, thefirst analogue signal is amplified and in step 153, the second analoguesignal is amplified. In step 154, the two amplified signals are combinedto double the amplitude of a single-carrier output signal to betransmitted. The procedure is ended in step 155.

The three flow diagrams exhibit large resemblances. The changes in thedifferent steps are of such a character, that it can be changed by e.g.software as a response on e.g. the modulation information given. Suchinformation can be provided on a time-slot basis, i.e. the requestedmodulation can be changed from one time-slot to the next. This impliesthat also the different operational modes of the present inventionpreferably are interchangeable from one time-slot to the next.

Some modifications of the above embodiments are also interesting to bedisclosed. In FIG. 10, another embodiment of a double transmitterarrangement according to the present invention is illustrated. Mostparts are identical to the ones in the first illustrated embodiment, andwill not be discussed again. However, some clear differences arepresent. First of all, it can be noted that in the previous embodiment,identical modulation and separation operations are performed in parallelin the first and second modulation units 50, 70. This can be avoided bythe present design, in which the second modulation unit 70 does notexplicitly have any separator. Instead, a connection 66 connects theoutput for the second component of the separator 65 in the firstmodulation unit 50 with the input of the analogue signal generator 76 ofthe second modulation unit 70. In this manner, the second modulationunit 70 can be made somewhat simpler and the computational effort duringthe operation is concentrated to the first modulation unit 50. Aconnection 67 also connects the output of the GMSK modulator of thefirst modulation unit 50 with the input of the analogue signal generator76 of the second modulation unit 70. This enables the correspondingsimplification to be performed for the TCC operation.

FIG. 11 illustrates a flow diagram corresponding to the 8PSK operationwith the embodiment of FIG. 10. Since the steps present are identicalwith some of the steps of the procedure of FIG. 8 they are not discussedagain. Basically, the steps 126 and 128 are omitted and the steps 121and 123 are changed into steps 122 and 124 respectively, in which onlythe first transmitter unit is involved. The second component used instep 131 is in this embodiment, however, provided from the firstmodulation unit.

FIG. 12 illustrates a flow diagram corresponding to the TCC operationwith the embodiment of FIG. 10. Since the steps present are identicalwith some of the steps of the procedure of FIG. 9 they are not discussedagain. Basically, the step 146 is omitted and the steps 141 and 143 arechanged into steps 142 and 144 respectively, in which only the firsttransmitter unit is involved. The second modulated signal used in step151 is in this embodiment, however, provided from the first modulationunit.

Now returning to FIG. 6. In this embodiment, the phase shifting of thesignal provided to the first power amplifier 64 was based on ameasurement of the power of the hybrid combiner load 92. Since there isa complementary relationship between the power to the transmitter device91 and the load 92, either power can be measured and the other can becalculated. Measuring the load power is a relatively easy task, but ofcourse, a direct measuring of the power supplied to the transmitterdevice is possible. The evaluation performed in the phase shifter 63 hasof course to be changed accordingly.

The phase shifting during TCC operation is relatively straight-forward.The power dissipated in the load 92 is minimised, and the two signalsare thereby phase-synchronized. However, in the case of 8PSK operation,the possible manners of performing the phase-shifting are less obvious.In a system, where the flexibility of the present invention is fullyused, the character of the transmitted signals varies. If TCC operationappears occasionally, the phase-shifting can be calibrated during suchTCC time slots. The values of the optimum phase shift can then bestored, e.g. in the phase shifter 63, to be used e.g. during 8PSKoperation.

The situation may, however, be somewhat more complex if the arrangementis designed also for frequency hopping. In FIG. 18, a part of a doubletransmitter arrangement according to the present invention isillustrated. The analogue signal generator 56 of the first modulationunit 50 is illustrated to have access to two different frequencygenerators 61A and 61B. A switch 68 connects one frequency generator ata time to the quadrature modulator 57. In the meantime, the otherfrequency generator is controlled to be tuned to the next frequency touse. When the frequency change is to be carried through, the switch 68selects the next frequency generator. Each frequency used may influencethe amplifier equipment to give different phase shifts. This means thatthe phase shift applied to the signal to be amplified in e.g. TCC or8PSK mode has to be calibrated at that particular frequency. If thephase shifts are calibrated during TCC mode and stored to be used in8PSK mode, there has to be one phase shift value for each frequency usedby the arrangement. Also, the two frequency generators 61A and 61B maygive rise to different phase shifts, whereby one calibrated phase shiftfor each combination of frequency generator and frequency is needed. Asignal can be sent from the frequency generators 61A, 61B to the phaseshifter 63 by a connection 86, for instructing the phase shifter whichphase shift to apply.

A storage 87 of phase shifts, e.g. comprised in the phase shifter 63 canbe configured as illustrated by FIG. 19. The storage 87 is here designedas a look-up table, with two input variables, identity of frequencygenerator used and the frequency of that frequency generator.

There are also alternative ways of obtaining calibrated phase shifts forthe 8PSK operation. These are necessary in cases there are no or veryfew TCC time slots. If only one power measure is available, e.g. thepower dissipated in the load 92 (FIG. 8), there has to be some inherentknowledge of the expected power to the transmitter device. In FIG. 13, aPVT (Power Versus Time) mask for 8PSK modulated normal burst is shown.The PVT mask defines the envelope range in which the 8PSK signal isallowed to vary. At a short time period before 200 and after 202 themain signal period 204, the maximum and minimum power curves areseparated by only 2.4 dB. This implies that without any knowledge of theactual system, the actual power of the signal is known with an accuracyof at least 2.4 dB. However, in most cases, design considerations areknown and the accuracy of the power is generally much higher, in atypical case 0.3-0.5 dB. By performing an output power measurementduring at least one of these periods a calibration of the phase shiftcan be achieved, even though the main signal is of a non-constantenvelope type. The power level in this period has a known relationshipto the average power over the entire burst. If the phase error of theamplifier varies with output power, the maximum value for the envelopewill be in phase, while the phase shift at dips in the envelope maydiffer. The phase shift monitoring is thus performed during a period oftransmission of a constant amplitude signal within a non-constantenvelope signal.

If any correction of the phase shift is needed, a correction of thephase shift added to the first signal is preferably performed when nouseful signal is transmitted from the transceiver device, e.g. during aguard period between two time slots. Since the guard time is long enoughto perform all setting procedures for the new phase shift, this willensure that the signal transmitted during the following time slot doesnot have any defects caused by a phase-shifting in progress.

In the above case, an a-priori knowledge about the expected amplitude ofthe transmitted signal is required. However, in more generaltransmission situations, such knowledge is not always available. In FIG.14, another embodiment of a power meter 93 is illustrated. Only parts,which are directly involved, are illustrated. In this embodiment, thepower meter 93 is still connected to measure the power over the load 92.However, the power meter 93 now also is supplied with signals from afirst and a second power sensor 96, 97, measuring the output power fromthe power amplifiers 64 and 84, respectively. In this manner, the powermeter can keep track on the power entering the hybrid combiner and thepower exiting from it. A signal corresponding to$1 - \frac{P_{L}}{\left( {P_{TX1} + P_{TX2}} \right)}$where P_(L) is the power dissipated over the load and P_(TX1) andP_(TX2) are the powers of the amplifier outputs. This quantitycorresponds to the cosine factor between the signals from the poweramplifiers. The phase shifter 63 (FIG. 6) can then according to thisadjust any phase shift, if necessary. Such an arrangement may be veryuseful, e.g. if downlink power control is applied.

By measuring also the power of the components, it becomes possible toperform calibration of the phase shift also during periods in whichnon-constant envelope signals are transmitted. However, performing itduring an arbitrary signal section induce a lot of problems. Onesolution is, however, to use signal sections of a-priori known digitalcontent. When transmitting a time slot of data using e.g. GMSKmodulation or 8PSK modulation, a section of “training symbols” isincluded in the data. This is schematically illustrated in FIG. 15.These training symbols are well-known and an expected output signal caneasily be calculated. By monitoring power values according to FIG. 14,during the transmission of such training symbols, an actual outputsignal can be compared with the expected one, and a phase difference canbe detected and used for calibration purposes.

Above, one embodiment of shifting the phase of a signal is illustrated.However, anyone skilled in the art understands that also otherphase-shifting devices and methods can be employed in order to achievethe functions of the present invention. When operating in a TCC mode,one attractive alternative arises. FIG. 16 illustrates some selectedparts of a transmitter arrangement having an alternative phase-shiftingarrangement. The power meter 93 is as before connected to a phaseshifter 63. However, in this embodiment, the phase shifter 63 isdirectly connected to the GMSK modulation means in the DSP 52. The phaseshifter 63 evaluates the power signals from the power meter 93 andprovides a requested phase shift AO to the GMSK modulation means 54. TheGMSK modulation means 54 uses typically a tabulated state machine 98operating according to a transfer function between the phase shiftinduced by the digital signal and time. A graph of such a function isillustrated in FIG. 17. The transfer function is draw with a full lineand denoted by 210. By simply adding the phase shift Δθ provided by thephase shifter 63 to the value achieved from the transfer function, theentire signal will be provided with an additional phase shift. Thephase-shift compensated transfer function will then look like the brokenline 212.

In the above embodiments, the DSP's 52, 72 have comprised oneconstant-envelope modulation means and one non-constant envelopemodulation means, in the form of a GMSK modulator and an 8PSK modulator.The DSP's may also comprise different types and different number ofmodulators. Other types of phase shift keying, such as 4PSK, areexamples of possible other non-constant envelope modulators.

Another interesting non-constant envelope modulator that can be used inthe present invention is a modulator for combined carrier signals. Oneembodiment of such a multi-carrier modulator is illustrated in FIG. 20.Here, two carriers of a GMSK modulation are combined, but it is alsopossible to combine carriers of other modulation schemes, e.g. 8PSK.Also, it is possible to combine carriers having different modulationschemes, e.g. one GMSK and one 8PSK carrier. Moreover, the basic ideasof this carrier combining can be generalized into more that twocarriers. However, in such cases, bandwidth restrictions may set apractical limit.

The DSP 52 comprises a carrier combiner modulation means 220, in thepresent embodiment in turn comprising two GMSK modulators 54A, 54B. Oneof the outputs of the selector 55 is connected to the first GMSKmodulator 54A. The first GMSK modulator means 54A is thus provided withthe digital signal provided by the input 51, which represents the signalintended for the first carrier. An additional digital signal input 228is provided to the second GMSK modulator 54B, whereby this modulator isprovided with a digital signal, which represents the signal intended forthe second carrier. An additional information input 222 is provided,which carries data defining a frequency difference between the twocarriers, or in the present embodiment half this frequency difference.The digital signals are GMSK-modulated separately into digital I and Qrepresentations. The I and Q representation from the first GMSKmodulator 54A is then modulated in a pre-modulator 225 with a signalhaving half the difference frequency provided by input 222, but with anopposite phase direction, i.e. in practice minus half the differencefrequency. The I and Q representation from the second GMSK modulator 54Bis similarly modulated in a pre-modulator 226 with a signal having halfthe difference frequency provided by input 222. The digital I and Qsignals are finally added in a summing means 224, providing a signalrepresenting two digital signals on one carrier each, pre-modulated tofrequencies of ±Δf/2. The up-conversion of the frequency, taking placelater in the chain, the frequency is selected to be the mean frequencyof the two carriers.

The digital signals resulting directly from the GMSK modulators 54A, 54Bare constant envelope signals. However, after the pre-modulation by thedifference frequency, they exhibit a non-constant envelope behavior. Thecomplex sum of these two signals is also of a non-constant envelopecharacter. In analogy with the 8PSK case described above, it is possibleto separate this sum signal into two components 31, 32 with constantenvelopes (cf. FIG. 4). The process then continues in analogy with the8PSK case described further above.

By using this scheme, any arbitrary combination of modulation schemes inany number of carriers can be combined and processed as a non-constantenvelope signal. Since the choice of modulation schemes furthermore canbe performed on a time slot basis, this opens up for a very highflexibility in the use of the transceiver unit arrangement according tothe present invention. However, there are also some drawbacks present.First of all, since the frequency difference between the carriers ismodulated into the signal even before the separation into components,the bandwidth of the signals that has to be treated throughout thetransceiver unit path is increased. The increase in bandwidthcorresponds approximately to the frequency difference. This puts veryhigh demands on the components in the transceiver unit, in particular onthe DAC's. There are, however, already today DAC components that wouldbe able to handle at least neighboring frequencies. Using more than twocarriers will of course make the bandwidth requirements even larger.

Another problem is that, if using more than two carriers, the outputpower per carrier will decrease. Since the total power is restricted bythe sum of the power of each individual transceiver unit, this maximumpower can not be exceeded. When having three or more carriers, the sumsignal 15 has to be scaled down in order to assure that it can beseparated into components, i.e. it has to be kept within double thecomponent amplitude. In order to be absolutely sure that every possiblecombination will be covered, the output power of each carrier will bereduced by a factor n/2, where n is the number of carriers.

The principle of separating a non-constant envelope signal into constantenvelope components opens up for a very flexible use of the transceiverunits. However, this principle is not very power efficient when handlingsignals of low amplitude. Even if the total signal has a low amplitude,the components have high amplitudes, which means that a large portion ofthe power will be wasted when re-combining the components in the hybridcombiner. A large power will dissipate through the load.

Also, when the total signal has a low amplitude, small changes in thesignal may cause very large phase changes of the components. Thebandwidth necessary to process the components will therefore be largerwhen the total signal has a low amplitude.

A way to reduce the problems described above is to renounce the demandof keeping the component amplitude constant. By letting the componentamplitude decrease when the total signal amplitude becomes small, someadvantages are achieved. The required bandwidth will decrease and thetotal power efficiency will increase. However, since the presentinvention is intended to operate also with amplifiers not beingperfectly linear, such component amplitude variations have to be keptwithin certain limits.

Another aspect to consider when deciding the reduction of the componentamplitudes is the efficiency of the power amplifiers. Most poweramplifiers exhibit the highest efficiency at the highest output values.A too large reduction in component amplitude will indeed result inhigher efficiency in the combiner stage, but may reduce the efficiencyin the power amplifier even more. The component amplitude reduction isthus preferably performed to optimize the allover efficiency.

As described in the above embodiments, there are a number of interestingadvantages arising by using the present invention. One of the mainadvantages is the high flexibility in using the arrangement. A user mayeasily, even on a time slot basis, change between different transmittingconfigurations. It is thus possible to change e.g. between high capacityand high output power, depending on the actual need. No re-calibrationshave to be performed and the changes typically involve solely softwarechanges.

It will be understood by those skilled in the art that variousmodifications and changes may be made to the present invention withoutdeparture from the scope thereof, which is defined by the appendedclaims.

REFERENCES

-   S. Mann, M. Beach, P. Warr and J. McGeehan, “Increasing the    talk-time of mobile radios with efficient linear transmitter    architectures”, Electronics & Communication Engineering Journal,    April 2001, Vol. 13, No. 2, pp. 65-76.-   U.S. Pat. No. 5,990,734.

1. Transmitter arrangement, comprising: a first modulation unit having afirst digital signal processor and a first analogue signal generator;said first digital signal processor having a first digital signal input;a first power amplifier, connected to an output of said first analoguesignal generator; a second modulation unit having a second digitalsignal processor and a second analogue signal generator; said seconddigital signal processor having a second digital signal input; a secondpower amplifier, connected to an output of said second analogue signalgenerator; combiner device connected to outputs of said first and secondpower amplifiers; and transmitter device connected to an output of saidcombiner device, said first digital signal processor further comprisesat least one first non-constant envelope modulation means; a firstsignal component separator connected to an output of said at least onefirst non-constant envelope modulation means; a first output of saidfirst signal component separator being connectable to said firstanalogue signal generator; first means for receiving modulationinstructions; at least one first constant envelope modulation meansconnectable to said first analogue signal generator; and firstmodulation selecting means for connecting a modulation means to saidfirst digital signal input in response to received modulationinstructions.
 2. Transmitter arrangement according to claim 1, whereinsaid second digital signal processor further comprises: at least onesecond non-constant envelope modulation means of the same type as saidat least one first non-constant envelope modulation means; and a secondsignal component separator connected to an output of said at least onesecond non-constant envelope modulation means; an output of said secondsignal component separator being connectable to said second analoguesignal generator; a sum of a signal of said first output of said firstsignal component separator and a signal of said output of said secondsignal component separator being equal to a signal of said output ofsaid at least one first non-constant envelope modulation means. 3.Transmitter arrangement according to claim 1, wherein a second output ofsaid first signal component separator being connectable to said secondanalogue signal generator.
 4. Transmitter arrangement according to claim1, wherein said second digital signal processor further comprises:second means for receiving modulation instructions; at least one secondconstant envelope modulation means connectable to said second analoguesignal generators; and second modulation selecting means for connectinga modulation means to said second digital signal input in response toreceived modulation instructions.
 5. Transmitter arrangement accordingto claim 4, wherein said first and second modulation selecting means areoperable on a time slot basis.
 6. Transmitter arrangement according toclaim 1, further comprising: first power monitor sensing a total powerto said transmitter device or a quantity directly related thereto; andphase-shifter connected to said first power monitor, arranged forcausing a phase shift of an analogue signal generated by said firstanalogue signal generator in response to said sensed total power. 7.Transmitter arrangement according to claim 6, wherein said first powermonitor is a power meter of a load of said combiner device. 8.Transmitter arrangement according to claim 6, wherein said phase-shiftercomprises means for complex multiplication of said phase shift with adigital signal to be inputted to said analogue signal generator. 9.Transmitter arrangement according to claim 6, using GMSK modulation,wherein said phase-shifter comprises means for introducing a phaseoffset in said GMSK modulation, generated by using a table driven statemachine in said first digital signal processor.
 10. Transmitterarrangement according to claim 6, further comprising means for providingsaid first and second digital inputs with the same digital signal, andsaid first and second means for receiving instructions with the sameinstructions of a constant envelope modulation, allowing transmittercoherent combining.
 11. Transmitter arrangement according to claim 6,further comprising: second power monitor sensing a power on said outputof said first power amplifier and being connected to said phase-shifter;and third power monitor sensing a power on said output of said secondpower amplifier and being connected to said phase-shifter; saidphase-shifter being arranged for causing a phase shift in response to acomparison between said sensed total power and said sensed power on saidoutput of said first and second power amplifier, respectively. 12.Transmitter arrangement according to claim 1, wherein that said firstand second non-constant envelope modulation means are selected from thelist of: 4-PSK modulation means; 8-PSK modulation means; and means forcombination of at least two carriers.
 13. Transmitter arrangementaccording to claim 4, wherein said first and second constant envelopemodulation means are GMSK modulation means.
 14. Method for generating atransmitter signal in a transmitter arrangement having at least a firstand a second modulation unit arranged in parallel, each one allowing forat least one non-constant envelope modulation and at least one constantenvelope modulation, said first modulation unit having a first analoguesignal generator, said second modulation unit having a second analoguesignal generator, comprising the steps of: providing digital signal tosaid first and second modulation units; providing modulation informationto said first and second modulation units; creating a first input signalto said first analogue signal generator by performing a constantenvelope modulation of a first digital signal provided to said firstmodulation unit as a response of said modulation information being arequest for a constant envelope modulation, and by performing anon-constant envelope modulation of said first digital signal andseparating a first component of said non-constant envelope modulatedfirst digital signal as a response of said modulation information beinga request for a non-constant envelope modulation; creating a secondinput signal to said second analogue signal generator by performing aconstant envelope modulation of a second digital signal provided to saidsecond modulation unit as a response of said modulation informationbeing a request for a constant envelope modulation, and by performing anon-constant envelope modulation of said first digital signal andseparating a second component of said non-constant envelope modulatedfirst digital signal as a response of said modulation information beinga request for a non-constant envelope modulation; generating a firstoutput signal in said first analogue signal generator according to saidfirst input signal; generating a second output signal in said secondanalogue signal generator according to said second input signal;amplifying said first output signal; amplifying said second outputsignal; combining said first and second amplified output signals to forman analogue transmitter signal.
 15. Method according to claim 14,wherein said providing steps are performed on a time slot basis. 16.Method according to claim 14, wherein said modulation informationcomprises a request for a non-constant envelope modulation, whereby saidstep of creating a second input signal to said second analogue signalgenerator is performed on said first signal in said first modulationunit, said method comprising the further step of transferring of saidsecond input signal from said first modulation unit to said secondanalogue signal generator.
 17. Method according to claim 14,characterized in wherein said modulation information comprises a requestfor a non-constant envelope modulation, and said second digital signalis identical with said first digital signal, whereby said step ofcreating a second input signal to said second analogue signal generatoris performed on said second signal in said second modulation unit. 18.Method according to claim 16, wherein said non-constant envelopemodulation is a 8-PSK modulation.
 19. Method according to claim 16,characterized in that said non-constant envelope modulation is amultiple-carrier GMSK modulation, whereby said method comprises thesteps of providing a set of at least two digital signals to both saidfirst and said second modulating units, whereby said creating stepscomprise the steps of performing a GMSK modulation of each digitalsignal and digital combining said modulated signals to form anon-constant envelope multi-carrier signal, whereby said separating stepis performed on said non-constant envelope multi-carrier signal. 20.Method according to claim 14, wherein said modulation informationcomprises a request for transmitter coherent combining of a constantenvelope modulation signal, and said first digital signal is identicalwith said second digital signal.
 21. Method according to claim 16,comprising the further steps of: monitoring a power of said analoguetransmitter signal or a quantity directly related thereto; and shiftinga phase of said first output signal according to said power.
 22. Methodaccording to claim 21, wherein said monitoring step comprises the stepof measuring a power rejected during said combining step, whereby saidpower of said analogue transmitter signal is provided as a complementaryquantity.
 23. Method according to claim 21, wherein said shifting stepin turn comprises the step of adjusting an initial offset phase of saidfirst or second modulating in a guard period between two time slots. 24.Method according to claim 21, wherein said shifting step in turncomprises the step of adding a phase shift in connection to thegeneration of the first output signal.
 25. Method according to claim 16,wherein said monitoring and phase shifting is performed when a constantenvelope modulation with transmitter coherent combining is used, wherebysaid phase shifting is preserved when selecting a non-constant envelopemodulation.
 26. Method according to claim 16, wherein said monitoringand phase shifting is performed during transmission of a constantamplitude period of a non-constant envelope signal.
 27. Method accordingto claim 16, comprising the further step of measuring instantaneouspower of said first and second analogue output signals, whereby saidshifting is performed according to a comparison of said power of saidanalogue transmitter signal and said power of said first and secondanalogue output signals.
 28. Method according to claim 27, wherein saidshifting in the case of transmitter coherent combining is performedaccording to:φ_(shift)=cos⁻¹(P _(TR)|(P _(TX1) +P _(TX2))), where P_(TR) is saidtotal power and P_(TX1) and P_(TX2) are said power of said first andsecond analogue output signals, respectively.
 29. Method according toclaim 27, wherein said comparison is performed during a period of aknown training sequence in a time slot.
 30. Method according to claim14, comprising the further steps of: reducing envelopes of said firstand second signals when said modulated signal has a low amplitude. 31.Method according to claim 30, wherein said step of reducing envelopescomprises minimizing of power consumption.
 32. Method according to claim14, comprising the further step of: storing an adjusted phase shiftvalue for each one of a set of used frequencies.
 33. Method according toclaim 32, comprising the further step of: storing an adjusted phaseshift value for each one of a set of used frequency generators for eachof said used frequencies.